1. Field of the Invention
The present invention relates to a method for the conversion of coal to recover energy value from the coal while minimizing waste by-products from the conversion process. The method can advantageously be utilized to convert very low-grade coal to products having high-energy value without emitting high levels of pollutants into the atmosphere.
2. Description of Related Art
Recently, the United States and other countries have experienced a shortage of natural gas and as a result, natural gas prices for consumers have increased substantially. Accordingly, there is a pressing need for economic methods for the manufacture of a high-value heating gas that can be used in place of natural gas. Natural gas has in composition that includes about 85 percent methane (CH4), about 10 percent ethane (C2H6) and the balance including propane (C3H8), butane (C4H10) and nitrogen (N2). Methane, the primary component of natural gas, has a heating value of about 51,623 Btu/lb.
In addition to being supplied directly to consumers, natural gas and other high BTU gas compositions can be utilized on-site to produce electricity. Further, there are many natural resources that are utilized to produce energy in addition to natural gas. For example, coal can be burned in conventional boilers to generate steam, which can be used to generate electricity. Many regions such as the United States, China and India possess vast reserves of coal that are not presently being exploited for current energy demands due to the high economic and ecological costs related to the use of the low-grade coal. Further, some of the coal deposits, particularly those found in India, contain high levels of contaminates and must be subjected to expensive processing prior to utilization. Alternatively, the off-gas from the boiler must be scrubbed to remove pollutants.
It is known to treat coal in a gasification process to convert the coal to a useful hydrocarbon product. For example, U.S. Pat. No. 3,700,584 Johanson et. al. is directed to the hydrogenation of low rank coal having a high oxygen content.
The prior art is generally directed to the direct conversion of the carbon in the coal to a hydrocarbon product, such as methane gas. Such processes have not proved to be economically and ecologically viable means for extracting energy value from coal.